Correction of incompetent venous valves

ABSTRACT

A cuff for restoring competence to an incompetent venous valve consists of a band of biocompatible implantable material that is not stretchable at blood flow pressures. The band is of sufficient length to encompass the vein at the site of the venous valve with the ends of the band overlapping. In one form of attachment, the end 22 passes over the loop 23 and is stapled thereto. The cuff can be attached to an applicator by means of the loop 23. A portion 26 of reduced thickness extends from the bottom face of the band to reduce any inner surface discontinuities with respect to the wall of the vein. 
     The cuff is placed around the vein at the site of the valve and the circumference of the cuff (and hence the diameter of the vein at the valve site) is reduced until competency of the valve in the vein is restored.

This application is a division of application Ser. No. 446,180, filedDec. 5, 1989 now abandoned, which is a continuation of application Ser.No. 191,168, filed as PCT/AU87/00215, Jul. 13, 1987 now Pat. No.4,904,254. .

FIELD OF INVENTION

This invention relates to the correction of incompetent venous valves.

Venous valves in mammals are usually bicuspid valves, with each cuspforming a sack or reservoir for blood which, under pressure, forces thefree edges of the cusps together to prevent retrograde flow of the bloodand allow only antegrade flow to the heart. When an incompetent valveattempts to close in response to a pressure gradient across the valve,the cusps do not seal properly and retrograde flow of blood occurs.

There are two chronic venous diseases in which incompetence of venousvalves is thought to be an important factor in the pathophysiology.These are varicose veins and chronic deep venous insufficiency.

The varicose vein condition consists of dilatation and tortuosity of thesuperficial veins of the lower limb and resulting cosmetic impairment,pain and ulceration. Primary varicose veins are the result of primaryincompetence of the venous valves separating the superficial venoussystem from the deep venous system. Secondary varicose veins occur asthe result of deep venous hypertension which has damaged the valves ofthe perforating veins.

Chronic deep venous insufficiency consists of deep hypertension of thelower limb with associated pigmentation, pain, swelling, ulceration andvaricose veins.

For the sake of convenience, the invention will be described in relationto the correction of incompetent valves in the venous system of thelower limb in man, but, it is to be understood that the invention is notlimited thereto.

The venous system of the lower limb consists essentially of thesuperficial venous system and the deep venous system. The superficialsystem includes the great saphenous vein and the small saphenous vein.The deep venous system includes the anterior and posterior tibial veinswhich unite to form the popliteal vein which in turn becomes the femoralvein when joined by the small saphenous vein.

The initial defect in primary varicose veins often involves localisedimcompetence of a venous valve thus allowing reflux of blood from thedeep venous system to the superficial venous system. This incompetenceis traditionally thought to arise at the saphenofemoral junction but mayalso start at the perforators. Thus, gross saphenofemoral valvulardysfunction may be present in even mild varicose veins with competentdistal veins. Even in the presence of incompetent perforators, occlusionof the saphenofemoral junction usually normalises venous pressure.

The initial defect in secondary varicose veins is often incompetence ofa venous valve secondary to hypertension in the deep venous system.Since this increased pressure is manifested at many points, correctionof one site of incompetence could clearly be insufficient as other sitesof incompetence will be prone to develop. Apart from the initial defect,the pathophysiology is similar to that of varicose veins.

Once the initial incompetence occurs, incompetence in other valves inthe system will tend to occur secondary to the venous hypertension.

Apparently, incompetence of venous valves is caused by dilatation of thevein wall. The evidence for this is as follows:

i) The valves in varicose veins are normal macroscopically andhistologically in most cases. The vein wall is more distensible inapparently normal veins in people with varicose veins.

ii) The valve cusps have a much greater tensile strength than the veinwall.

iii) Venous function deteriorates during the day as the venous systembecomes more dilated.

iv) Saphenofemoral valves which are incompetent can become competentagain at operation when the diameter is decreased by spasm. A similaroccurence has been noted in the superficial femoral vein.

v) Varicose veins may temporarily appear during pregnancy before theuterus is large enough to cause venous obstruction.

vi) Forearm veins which are incompetent when full and distended canbecome competent again when the distal segment is emptied thus reducingthe diameter. Valves which are competent can be made incompetent byinjection of local anaesthetic which caused venodilatation.

Thus, it appears that dilatation of the vein wall, whether idiopathic(primary varicose veins) or secondary to venous hypertension (secondaryvaricose veins) leads to valvular incompetence. This dilatation mayeventually lead to stretching and sclerosis of the valve. Other valvesin the system will tend to become incompetent as the reflux of bloodcauses dilatation of the vein wall. We have found that it is possible toreverse or prevent the destructive process by overcoming thisdilatation. Even if the vein wall weakness is generalised as appears tobe the case with primary varicose veins, correction of the initialdefect will delay or prevent stress being placed on that wall and thushinder progression of the disease.

The fundamental change in flow in primary varicose veins is reflux ofblood from the deep venous system into the superficial venous system,usually the great saphenous vein.

Traditionally, chronic deep venous insufficiency is regarded as beingsecondary to deep venous thrombosis which either obstructs the vein oris recanalised with associated destruction of the deep venous valves.The obstruction is initially prominent but as recanalisation occurs andcollateral circulation develops, the obstruction is less prominent. Thenthe venous incompetence becomes more prominent. This syndrome followsdeep venous thrombosis in a majority of cases.

Deep venous thrombosis is involved in the majority of cases ofpost-phlebetic syndrome but other factors such as site of deep venousthrombosis, obesity, muscle activity, posture and genetic predispositionmay be involved. A primary incompetence of the venous valves appears tobe involved in a significant number of cases.

BACKGROUND ART

In the main, prior art approaches to restoring competency of incompetentvalves has involved venous reconstruction surgery of three basic kinds,namely, venous valve transplants, venous transposition and venousvalvuloplasty.

As the term implies, the venous valve transplant approach involves thereplacement of the segment of the vein having the incompetent valve witha segment of another vein having a competent valve. The venoustransposition approach involves the redirection of the venous system soas to bypass an incompetent valve and venous valvuloplasty involvesvenous valve reconstructive surgery in which the free length of thevalve cusps is reduced by plicating sutures.

These approaches to the prior art are well documented in A RATIONALAPPROACH TO SURGERY OF THE CHRONIC VENOUS STASIS SYNDROME by HarrySchanzer AND E Converse Peirce ANNALS OF SURGERY 1982, 195: 25-29 aswell as in VALVULOPLASTY AND VALVE TRANSFER by Seshadri Raju Inter.Angio 4 1985 419-424.

A single example on one patient of an experimental technique fortreating an incompetent venous valve not involving the above types ofvenous surgery is described in an article by Dag Hallberg in ACTA CHIRSCAND 138: 143-145, 1972. Hallberg placed a band two to threemillimeters larger than the diameter of the view around the vein.

The band was made of DACRON polyester and polyester and was applied whenthe patient was in the horizontal position. The band was retainedloosely in position by several sutures in the venous adventitia.

Hallberg's method could not restore competence to the majority of theincompetent venous valves. In patients with venous disease, incompetentvalves will usually be incompetent in the horizontal as well as thevertical positions. See, for example, FEMORAL VEIN RECONSTRUCTION IN THEMANAGEMENT OF CHRONIC VENOUS INSUFFICIENCY by Ferris E. B. and KistnerR., ARCHIVES OF SURGERY, 1982, 117:1571-1579.

Ferris and Kistner operated on 53 femoral veins in which the valves hadbeen demonstrated pre-operatively to be incompetent. In only one casewas the valve noted to be competent when the patient was horizontal atthe time of operation. Kistner's approach was to suture the vein toprevent post-operative dilatation.

It is well known that by itself DACRON (Registered Trade Mark) polyestermaterial causes marked fibrosis as well as foreign body reaction.Therefore, DACRON polyester cannot alone be considered biocompatible. Infact, DACRON polyester has been employed to stimulate fibrotic reactionswhich incorporate the synthetic fabric into tissue (see: S. Raju, ANN.SURG. (1983) 197, 688-697).

The article REVASCULATION OF SEVERELY ISCHEMIC EXTREMITIES WITH ANARTERIOVENOUS FISTULA by F. W. Blaisdell et al in AMERICAN JOURNAL OFSURGERY, Volume 112, pages 166-173 discloses problems associated withthe use of DACRON polyester as an implantable material. In a number ofcases, gradual narrowing of arteriovenous fistulas under a woven DACRONpolyester sleeve was demonstrated.

In physical terms, the Hallberg approach was a static one. Once the cuffwas sutured into position, no attempt was made to reduce the diameter ofthe vein at the valve site to restore competency of the valve. Indeed,Hallberg's single patient experiment was concerned with furtherdilatation of the vein at the valve site rather than reduction in thediameter of the dilated valve to restore competency.

DISCLOSURE OF THE INVENTION

It is an object of this invention to provide a method for restoringcompetence of incompetent venous valves by reducing the diameter of theappropriate vein at the valve site.

It is a further object of the invention to provide a method forrestoring competence of incompetent venous valves in which the diameterof the vein at the valve site is adjusted to achieve proper competenceof the valve and which permits clinical testing at the time of diameterreduction.

It is a yet another object of the invention to provide a device forrestoring competence of an incompetent venous valve which isbiocompatible and which does not require suturing to the vein itself.

According to one aspect of the invention there is provided a cuff forrestoring competence to an incompetent venous valve, said cuffcomprising a band of biocompatible implantable material that is notstretchable at blood flow pressures, the band being of sufficient lengthto emcompass the vein at the site of the venous valve, with portions ofthe band overlapping, the overlapping portions being joinable togetherto form a cuff of desired circumference small enough to restorecompetence yet not too tight to decrease blood flow.

According to another aspect of the invention there is provided a methodof restoring competency to incompetent venous valves comprising thesteps of:

i) placing a cuff of biocompatible material around the vein at the siteof the valve,

ii) reducing the circumference of the cuff (and hence the diameter ofthe vein at the valve site) until competency of the valve in the vein isrestored, and,

iii) fixing the circumference of the cuff at the point where thediameter of the vein is reduced to restore competency of the valvewithout impairing blood flow.

If necessary, the cuff is then secured to the surrounding tissue.Preferably, the circumference of the cuff around the vein is reduced ina stepwise fashion with the competency of the valve being tested betweeneach stepped reduction in the circumference of the cuff. Competency ofthe valve may be tested by milking the vein, by the use of appropriatepressure detectors or by Doppler Techniques.

BRIEF DESCRIPTION OF THE DRAWINGS

In order that the invention may be more readily understood and put intopractical effect, reference will now be made to the accompanyingdrawings in which:

FIG. 1 is a cutaway diagrammatic perspective view of one side of a veinat a valve site with the valve in its closed disposition,

FIG. 2 is a plan view from above of the venous valve shown in FIG. 1,

FIG. 3 is a schematic view of a competent venous valve in its closeddisposition,

FIG. 4 is a schematic view similar to FIG. 3 but of an incompetentvalve,

FIG. 5 is a perspective view of a venous cuff according to oneembodiment of the invention,

FIG. 6 is a perspective view of the cuff shown in FIG. 2 encircledaround a vein,

FIG. 7 is a plan view of a second embodiment of a venous cuff,

FIG. 8 is a side elevational view of the cuff shown in FIG. 3 in placeat the junction of two veins,

FIG. 9 is a plan view of a third embodiment of a venous cuff,

FIG. 10 is a side elevational view of the cuff shown in FIG. 5 in placeat the junction of two veins,

FIG. 11 is a graph of distal blood pressure against circumference of avein at a valve site, and,

FIG. 12 is a graph of retrograde resistance against vein circumferenceat a valve site.

DESCRIPTION OF PREFERRED EMBODIMENTS

The valves in the venous system of man are almost invariably bicuspid asis shown diagramatically in FIG. 1. Each cusp 10, 11 is semi-lunar andis attached to the wall of the vein 12 by its convex edge 13. Theconcave edges 14 lie free in the direction of normal blood flowindicated by arrow F. The attachment of each cusp approaches that of theother cusp proximally to form the commissure 15. Proximal to the valve,the vein is more distensible for about 1 cm. to form the sinus. Incross-section, when closed, the cusps 10, 11 of the valve meet in astraight line in the centre of the vein 12 as shown in FIG. 2.

It will be appreciated that the venous valve is normally open with thefree concave edges 14 separated by the upward flow of blood in thedirection of arrow F. As will be apparent from FIG. 1, each cusp 10, 11forms a sack or reservoir 16 for blood which, under pressure, in thedirection of arrow R, forces the concave edges 14 together to preventretrograde flow of blood--see FIGS. 1 and 3.

There are 10 to 20 valves in the great saphenous vein and 7 to 13 in thesmall saphenous vein. The perforating veins also have valves except forthe feet where they are unusual.

On standing at rest, the pressure in both the superficial and deepvenous system correlates closely with the hydrostatic pressure of acolumn of blood at the height of the atrium, about 80-90 mm. Flow inboth superficial and deep systems is slow and is directed towards theheart (antegrade). Flow in the perforators is also slow but tends to befrom the superficial venous system to the deep venous system. The flowin the foot is the reverse of that just described--from the deep veinsin the sole of the foot to the superficial veins on the dorsum of thefoot.

The position changes markedly on exercise. On calf contraction (systole)the pressure and flow in the deep system increases and flow through theperforators ceases. On calf relaxation (diastole) the pressure and flowin the deep system decrease and there is increased flow in theperforators from the superficial venous sytem to the deep venous system.The mean venous pressure drops during exercise by about 60-70 mmHg.

These changes are the result of the musculo-venous pump. As the musclecontracts, blood is expelled towards the heart. The blood is preventedfrom moving into the superficial system by the valves in the perforatingsystem. On relaxation of the muscle the pressure drops but blood isprevented from reflux by the valves of the deep venous system and flowrecommences from the superficial venous system to the deep venoussystem, through the perforators. The musculo-venous pump is responsiblefor efficient venous return in combination with the vis a tergo effectand of intra-thoracic and intra-abdominal pressure.

A competent valve is shown diagramatically in FIG. 3 in its closeddisposition and an incompetent valve in FIG. 4. The cusps 10 and 11 ofthe competent valve in FIG. 3 form the blood sacks 16. The length ofvein 12 at the valve site is indicated by "L" and the diameter of thevein, when the valve is competent, is indicated by "d". The extent ofcontact of the upper edges of the cusps when the valve is closed isindicated by "1".

When the diameter of the vein 12 is increased to "D" as shown in FIG. 4,the concave edges 14 of the cusps no longer meet and retrograde flow ofblood can occur. The cusps 10a, 11a shown in dotted outline in FIG. 4represent the normal disposition of the cusps and thus it can be seenthat dilatation of the vein has led not only to separation of the cuspsbut also to a decrease in the general angle of the cusps to one anotherwith a consequent lessening of the possible area of contact between thecusps should contact be possible at some diameter less than "D".

According to the present invention, it is possible to restore competenceto an incompetent valve by decreasing the diameter of the vein wall atthe valve site from the valve "D" of FIG. 4 towards but not necessarilyto the diameter "d" of FIG. 3 by the use of a venous cuff.

The venous cuff 20 shown in FIGS. 5 and 6 is made of a bio-compatiblematerial that does not significantly react with a vein or its surroundsand which in this instance, is flexible but does not stretch at thepressures encountered in blood flow. A preferred material is siliconerubber sheeting reinforced with embedded polyester fibres.

The venous cuff 20 consists of an elongated band 21 having a free end 22and a loop 23 at its other end 24. As can be seen in FIG. 5, the loop 23extends above the upper face 25 of the band 21 so that it may receivethe free end 22 as shown in FIG. 6.

The loop 23 may be formed as a separate item that is glued to the band21. In this instance, the loop 23 is formed from a flat rectangularstrap 26 of polyester reinforced, Dow Corning Medical Grade siliconerubber sheet No. 501-1. The flat strap 26 has two straight slits 27extending inwardly from the opposite edges of the strap and cut parallelto and 2 mm from the longitudinal side 28. The dimensions of the strap26 according to one embodiment (which are given for illustrativepurposes only) are as follows:

Length: 48.0 (±0.5) mm

Breadth: 5.0 (±0.2) mm

Thickness: 0.178 (±0.076) mm

Slit length: 16.7 (+2-0.0) mm

The slits 27 divide the loop 23 into an inner attachment portion 29 thatis 2 mm wide and an outer deformable portion 30 that is 3 mm wide. Thefree ends of the attachment portion 29 are folded over one another toprovide the loop 23. The free ends of the deformable portion 30 are eachfolded over themselves and secured between each folded portion by meansof a suitable adhesive is a securing tab 31 by means of which the cuffmay be sutured to neighbouring tissue.

In this instance, the band 21 is formed from a flat piece of polyesterreinforced Dow Corning Medical Grade silicone rubber sheet No. 501-3. Ahole 32 may be cut in the tapered end 22 of the band 21 for attachingthe band 21 to a mechanical applicator. The dimensions of the band 21according to one embodiment which are given for illustrative purposesonly are as follows:

Length: 68.0(±0.5) mm

Breadth: 15.0(±0.5) mm

Thickness: 0.503(±0.076) mm

Taper Length: 20.0(±0.5) mm

Taper Breadth: 10.0(±0.5) mm

Hole diameter: 3.0(±0.2) mm

As will be apparent from the above dimensions, the deformable portion 30is made from thinner material than the band 21 in order to decrease anypossible effects that cuff surface discontinuities may have on the veinwall. The use of thinner material for the deformable portion 30 allows asmooth overlap inner surface on the cuff when implanted around a vein asis shown in FIG. 7 and allows the cuff to assume the shape of the vein.

As will be apparent from FIG. 6, with manual application of the cuff,the loop end 24 of the band 21 is placed on the vein 33. The band 21 isthen encircled around the vein 33 and the free end 22 of the band 21 ispassed through the loop 23. When the circumference of the cuff has beenreduced to the point whereat the diameter of the vein is reduced torestore competency of the valve within the vein 33, the overlappingportions of the band 21 are fixed together by stapling or suturing and,if necessary, the free end 22 of the band 21 beyond the suture or stapleis removed by any convenient means. The tabs 31 are then sutured totissue surrounding the vein to prevent the cuff from sliding along thevein.

In an alternative method of application, the band could be looped in theother direction so that the free end of the band overlies the top of theloop as shown in FIG. 8.

The modified form of the venous cuff shown in FIG. 7 is particularlysuitable for restoring the competence of a valve in a first vein havinga junction with a second vein of the kind shown in FIG. 8. The cuff issubstantially similar to that shown in FIG. 5 and thus common elementsshare the same numerals.

A cut out portion 40 in the upper edge 41 of the band 21 is sodimensioned to enable the cuff to assume the shape shown in FIG. 8 whenthe cuff is positioned around a first vein 42 adjacent to its junctionwith a second vein 43.

The portions 44 of the band 21 adjacent to the cut-out 40 engage thevein as shown in FIG. 8 and the cuff is secured in position by means ofone tab 31 being sutured to the tissue surrounding the vein 42 and theother tab 31 being sutured to tissue surrounding the vein 43.

The cuff shown in FIG. 9 is substantially similar to that shown in FIG.7 except that the cut-out 50 is in the lower edge 51 of the band 21. Thecut-out 50 is so dimensioned to enable the cuff to assume the shapeshown in FIG. 10 when the cuff is positioned around a first vein 52adjacent to its junction with a second vein 53.

The portions 54 of the band 21 adjacent to the cut-out 50 engage thevein 53 as shown in FIG. 10 and the cuff is secured into position bymeans of one tab 31 being sutured to tissue surrounding the vein 52 andthe other tab 31 being sutured to tissue surrounding the vein 53.

It will be appreciated that the venous cuff may be made of anyappropriate bio-compatible material that will not give rise to anysignificant adverse reactions within the body such as thrombosis,stenosis (i.e. narrowing of the vein) or perforation of the vein wallthrough wear and tear. The overlapping portions of the band 21 may besecured together in any convenient way--with or without the loop orbuckle arrangement shown in the drawings. The overlapping portions maybe secured together by stapling or suturing as described above, or bymechanical interlocking of parts of one portion with part of the otherportion of the band at the overlap, or by adhesive, or by heat sensitiveor pressure sensitive means.

If the overlapping portions of the band 21 are secured together by meansexternal of the band such as by staples, sutures or adhesives, theexternal means should be selected so that there is no adverseinteraction between the fastening means and the cuff or therein orsurrounding tissue. It is preferred that neither the band nor thefastening means be secured to the vein.

Although the above described cuffs incorporate tabs for securing thecuff to tissue surrounding the vein, such tabs are not essential.Anchoring of the cuff may not always be required--for example, thelocation of the cuff may not permit movement of the cuff along the veinor the material of the cuff may possess sufficient friction with respectto the vein so as to prevent movement of the cuff along the vein.

The cuff may, of course, be of any convenient shape or configuration. Asto its breadth (i.e. its dimension along the vein), the minimumrequirement is that the cuff should cover substantially all of the cuspsof the valve, preferably with some 1 to 1.5 mm excess at each end of thevalve. The maximum breadth is limited by the general consideration thata single cuff should not span two venous valves.

The band is to be long enough to encircle the vein to which it is to beapplied and to provide sufficient overlap to facilitate joining of theoverlapping portions. As will be explained in more detail below, theoverlapping arrangement of the band portions enables the circumferenceof the cuff to be reduced to the desired value at which competence isrestored. That is to say, the cuff is applied in a dynamic way--the cuffcircumference is initially larger than the diameter of the dilated veinand the circumference of the cuff is reduced until competency of thevalve is detected.

The cuff may be manufactured from components as described above orformed as a one piece moulding.

EXAMPLE 1

A use of the cuff will now be described in relation to incompetence ofthe sapheno-femoral valve. The function of the sapheno-femoral valve isto decrease the pressure in the long saphenous system.

When the sapheno-femoral valve becomes incompetent, the vein distal tothis point is exposed to abnormally high pressure which in turn causesdilatation of the vein below the sapheno-femoral valve and incompetenceof the corresponding valve. This sequence continues until thethin-walled tributaries of the internal saphenous vein are also exposedto pressures that cause them to dilate, elongate and becometortuous--that is to say, they become varicose.

The above described sequential process commences because of theincompetence of the valve at the sapheno-femoral junction. Thus, if thefunctional defect of the valve is corrected by surgery, the patient willbe substantially free from risk of further varicose veins.

The function of the cuff is to decrease the size of the sapheno-femoralvein at the valve site which pathologically dilates and, as describedabove, the consequent incompetence of the valve causes varicose veins.The cuff is tightened around the vein at the valve site until the valveis assessed, during the operation, as being competent.

The standard surgical approach to the sapheno-femoral junction is usedand the tributaries of the saphenous system are tied off before placingthe cuff in position.

The sapheno-femoral valve band is so dimensioned as to encircle thesapheno-femoral vein at the valve site with the ends of the bandoverlapping so that they can be secured together in any convenient way.The sapheno-femoral valve can usually be seen through the vein wall andthus the cuff can be correctly located by inspection.

An integral securing tab may be provided in the mid portion of the strapthat is preferably larger than the diameter of the vein at the valve.The securing tab may conveniently be of semi-circular shape and may besutured to the cribriform fascia above the sapheno-femoral valve usingfine non-absorbable sutures.

The use of the valve repairing cuff enables the main saphenous system tobe left intact so that it may be used for coronary artery by-passgrafting, femoro-popliteal by-pass grafting and any of the otherdifferent types of by-pass grafting used in standard vascular surgery.

The varicose veins that actually appear in the legs are tributaries ofthe main long saphenous system and are dilated and become tortuousbecause the walls of these veins are exceedingly thin. On the otherhand, the main long saphenous system itself has thick walls three tofour times as thick as its tributaries and indeed has more muscle in itswalls than any other vein in the body. Thus, this vein may be relativelynormal whilst its tributaries become dilated. The insertion of thevenous cuff at the sapheno-femoral junction preserves the long saphenoussystem and a standard removal of varicose tributaries can be performedat the same procedure.

EXAMPLE 2

It has been noted while using the venous cuff of the invention that therestoration of competence to a valve occurred rapidly at a criticalcircumference. A small increase in circumference resulted in a largeincrease in incompetence. Two studies examined this phenomenon, one invivo and one in vitro.

The first study was performed on the left internal jugular vein of asheep. A side to side arteriovenous anastamosis was performed proximalto a minimally incompetent valve. The vein was re-explored 2 weeks laterand the pressure gradient was measured across the valve. The proximalpressure was a mean of 90 mmHg. The distal pressure was measured acrossthe valve at different circumferences of the venous cuff. The initialcircumference was 4 cm. This is a reflection of the degree of competenceof the valve. The results were as follows:

                  TABLE 1                                                         ______________________________________                                        Venous Cuff Circumference                                                                        Distal Pressure                                            (cm)               (mmHg)                                                     ______________________________________                                        4.0                55                                                         3.6                36                                                         3.4                30                                                         3.3                24                                                         3.0                25                                                         2.8                22                                                         2.6                21                                                         2.5                24                                                         ______________________________________                                    

The venous pressure when the vein occluded was 23 mmHg which is theminimum pressure that the distal vein can achieve with a fully competentvalve or with a circumference of 0 cm.

FIG. 12 is a graph of the results in Table 1. It can be seen that onlyminimal improvement in competence can be made by reducing circumferencebelow 3.3 cm. That is, a 17.5% reduction in circumference produced anear maximal effect on competence. Any further reduction incircumference is unnecessary and increases the risk of obstruction. Theuse of a special applicator allows a fine adjustment in circumference tobe made and for competence to be continuously tested with successivesmall decreases in circumference.

EXAMPLE 3

The second study was on the right internal jugular vein of the samesheep. An in vitro set-up was used for this study. Hartmann's solution(Ringer's lactate) was perfused retrogradely from a standard intravenousinfusion set at a height of approximately 1 meter. The distal vein wasalso connected to plastic tubing which was raised to run into areservoir so that the distal pressure was a constant 5 mmHg. Pressureswere measured 1 cm above and below the valve using the same equipmentand methods as in the previous studies except that 19 G needles ratherthan cannulae were used.

The flow was measured using a measuring flask to measure outflow fromthe distal vein over 30 seconds. The results were as follows:

                  TABLE II                                                        ______________________________________                                        Venous Cuff            Pressure                                               Circumference                                                                             Flow       Gradient Retrograde                                    (cm)        (ml/min)   (mmHg)   Resistance                                    ______________________________________                                        3.6         146         2       0.01                                          3.0         81          5       0.06                                          2.6         5          80       16.0                                          2.5         3          90       30.0                                          ______________________________________                                    

There was no increase in competence with further decreases incircumference unless the vein was occluded. The results shown in TableII are graphed in FIG. 12. Although insufficient points are plotted tobe confident as to the exact best fitting curve, it is apparent that alarge change in retrograde resistance is produced within a small rangeof change in circumference.

These studies on the biomechanics of the valve confirm the criticalnature of circumference on competence. A narrow optimal range isapparent in these studies and can be observed by the surgeon whileapplying the venous cuff. If the vein is narrowed beyond this point,then a relative obstruction may be produced for no gain in competence.The choosing of the optimal circumference is aided by the use of anapplicator which enable small increments in decreasing the circumferenceof the band and allows the surgeon to test competence by the "milking"technique. An optimal circumference can thus be found without narrowingthe vein unnecessarily.

EXAMPLE 4

A venous cuff according to the invention has been used to restorecompetence to incompetent valves in ten internal jugular veins of sheep.All ten valves required a reduction in circumference of the dilated veinto produce a satisfactory degree of competence as is shown in thefollowing table:

                                      TABLE III                                   __________________________________________________________________________               CIRCUMFERENCE PERCENTAGE DECREASE                                  SHEEP                                                                              JUGULAR                                                                             IN CMS.       IN                                                   NO   VEIN  INITIAL                                                                             WITH CUFF                                                                             CIRC.    AREA                                        __________________________________________________________________________    86   LEFT  2.9   1.9     34       57                                               RIGHT 2.5   2.1     16       29                                          87   RIGHT 3.5   2.2     37       60                                          88   LEFT  4.0   2.8     30       51                                               RIGHT 3.9   2.8     28       48                                          89   LEFT  2.6   2.2     15       28                                               RIGHT 2.7   2.0     26       25                                          90   RIGHT 1.9   1.5     21       38                                          91   LEFT  2.0   1.7     15       28                                               RIGHT 2.4   2.0     17       31                                          __________________________________________________________________________

The average reduction of circumference was 24% with a range of 15% to34%. This is a moderate degree of narrowing but it must be placed in thecontext that veins are normally in a partially collapsed state whencompressed by surrounding tissue. One vein was made incompetent bycreating an arterio-venous fistula which caused dilatation of the valvering. The reduction in circumference necessary to restore competence was52%.

The animal model of venous valve incompetence is a useful one because,

i) The venous valves in the internal jugular vein in sheep appearmacroscopically identical to the venous valves in humans. The histologyof the vein wall is also similar.

ii) The cause of the incompetence is the same as that which applies inover 90% of cases of varicose veins in at least 50% of cases of deepvenous disease in humans, that is, hydrostatic pressure overcoming thestrength of the vein.

iii) An arteriovenous fistula has been found to mimic venousinsufficiency in dogs, and has been used with proximal venous occlusionin dogs and rats. The arteriovenous fistula alone is sufficient toproduce swelling of the limb in dogs and lymph changes which are similarto the disease of humans. It is also well known that an arteriovenousfistula can produce varicosities in humans and ulceration even of theupper limb.

iv) The response of the vein wall histologically to a fistula hassimilarities to changes observed in saphenous veins in humans when usedas an arterial graft particularly in the intimal proliferation, veinwall fibrosis and variable damage to the internal elastic lamina. Thechanges are, however, less severe.

v) Destructive changes on the valve and vein wall are hastened both bythe continuous application of a very high pressure to the valve and alsoby the pulsatile nature of the pressure which is thought to have anadverse affect on collagen.

In two sheep, incompetence of the valves developed quickly (within 5days). This is despite the fact that these valves managed to remaincompetent for years (depending upon the age of the sheep) of normalfunction. The pressures on these valves normally would increase ongrazing, when the head is lowered. The valves would be subjected to thehydrostatic pressure from the right atrium to the valve. The valveswould also be subjected to pressures associated with coughing andValsalva type maneuvers.

The implantation of the venous cuff protected the distal vein from thehigh pressure of the arteriovenous fistula. This was demonstratedconvincingly by the measured pressure gradient and circumferences beforeand after implantation. In one sheep, this protective effect was stillpresent nearly 9 weeks later at harvesting of the vein. From the resultsin this sheep it could reasonably be expected that this protectiveeffect would last many years in the normal situation. This can be seenfrom the fact that the fistula had a destructive effect in five daysgreater than the life of the animal to that stage. Despite 9 weeks ofthis stress, the valve functioned well with the venous cuff implanted.

The venous cuff is very effective in preventing venous valveincompetence even in the presence of abnormally high pressures. Thesepressures created incompetence in the controls within two weeks yet thisdid not happen with the venous cuff in situ at a mean of 20 weeks. Theimportance of prevention of movement of the venous cuff along the veinled to the addition of tags or ears to the venous cuff to facilitateattachment to the surrounding fascia.

There was minimal damage to the vein wall and no complicationattributable to the venous cuff itself. Comparison of light microscopycontrol and implant results showed that negligible effects on the veinwall are attributable to the venous cuff.

The silicone rubber sheet venous cuffs produced a similar reaction inall cases of implants. The macroscopic reaction to silicone rubber sheetaround the adventitia of the vein was a smooth fine fibrous opaque whitereaction. The silicone rubber sheet lifted easily away from the vein.There was no incorporation of the silicone rubber sheet into the veinwall and there was a small amount of clear serous fluid between the wallof the vein and the silicone rubber sheet.

The macroscopic appearance was that of serous membrane. When the vessellumen was opened underneath the silicone rubber sheet cuff, there wasminimal thickening of the wall.

The intimal lining itself appeared macroscopically identical to thesurrounding intima. There was no evidence of any thrombotic process, noulceration, no fibrotic obstruction, no haemorrhage into the wall and nothickening of the vein wall. One sheep had a decrease in the diameter ofthe wall distal to the implant. This appeared to be related to asubcutaneous suture distally which was compressing the vein. This wasnot associated with the silicone cuffs themselves.

Based on microscopic observation, light microscopy, scanning electronmicroscopy and pressure measurements, the following conclusions can bedrawn from the above animal studies.

The venous cuff is made from a material with favourable biocompatibilitycharacteristics in terms of interactions with veins. There was minimalor no difference in histology of implant specimens and control specimenson the vein wall. Out of 50 implants in animals, there have only beenthree complications with two implants. There were two infections and onethrombosis. This thrombosis was probably caused by the pressuremeasurement technique. The two infections would be expected with anyoperation. The silicone cuff has not caused complications beyond thoseexpected with any similar operation with no implant. Thus nocomplication can be directly attributed to the cuff.

The venous cuff is highly successful at restoring competence toincompetent venous valves which are not destroyed by thrombophelbitis.Competence was markedly improved in all 20 of 20 valves in animalmodels. The improvement is maintained at a mean implant time of 12weeks. This is also supported by six implants which preventedincompetence despite very high retrograde pressure gradient for a meanimplant time of 20 weeks and a maximum of 28 weeks implant time.

The animal models are confirmed by the human work. The only complicationout of 16 implants was one infection which had no long-term morbidityafter removal of the cuff. There were two prophylatic implants. Theimplant of the cuff produced competence in twelve out of the remainingthirteen valves. The other valve was affected by thrombophlebitis, whichis now regarded as a relative contra-indication to the procedure. Ofthese thirteen valves, ten were for varicose veins and all patients hadresolution of symptoms. The mean implant time was 25 weeks. The longestimplant was 15 months. This long-term implant has had no recurrence ofan ulcer which was present five months continuous preoperatively. Theremaining three implants were on a patient with deep venous disease. Hehad healing of his ulcers and has minimal symptoms three monthspostoperatively.

The venous cuff of the invention is a safe, reliable device forproducing long-term competence in incompetent venous valves. Thisproduces a corresponding resolution of symptoms in people with varicoseveins and chronic deep venous insufficiency.

The venous cuff may be placed into position and tightened around thevein by the use of an applicator such as that described in ourAustralian patent application PI 0271 filed on Feb. 10, 1987. Such anapplicator has an upstanding tab which receives the loop of the cuff.The cuff is then passed around the vein and the free end of the cuffconnected to a cuff adjustor mounted on the applicator body with aratchet mechanism which allows the adjustor to be moved relative to theapplicator and to be held in any selected position. A stapling gunincorporated within the applicator is used to secure the overlapping endof the cuff to the loop 13.

As will be apparent from the above description, the applicator allows asingle surgeon to apply the cuff to a vein. With one hand, the surgeonusing the applicator can adjust the cuff to the desired diameter andthen test the valve for competence. After final adjustment of thediameter, the surgeon then staples the overlapping portions of the cufftogether. If need be, the free end of the band is trimmed and the cuffremoved from the applicator.

Various modifications may be made in details of the cuff and the methodof restoring venous valve competency without departing from the scopeand ambit of the invention.

I claim:
 1. A venous valve competence-restoring cuff, said cuffcomprising an elongated band, having one end and opposite overlappingend portions, of biocompatible implantable material, said materialhaving an elasticity such that it is not stretchable at blood flowpressures, the band having a length to encompass the vein at the site ofthe venous valve, with said end portions of the band overlapping, theend portions being joinable together to form a cuff of desiredcircumference small enough to restore competence yet not too tight todecrease blood flow, and further including loop means adjacent said endportion of the band to which said overlapping end portion of the band isjoined.
 2. A venous valve competence-restoring cuff, said cuffcomprising an elongated band, having one end and opposite overlappingend portions, of biocompatible implantable material, said materialhaving an elasticity such that it is not stretchable at blood flowpressures, the band having a length to encompass the vein at the site ofthe venous valve, with said end portions of the band overlapping, andmeans for securing the end portions together to form a cuff of desiredcircumference small enough to restore competence yet not too tight todecrease blood flow and further including loop means adjacent said endportion of the band to which said overlapping end portion of the band isjoined.
 3. A cuff according to claim 1 or claim 2 and further includingmeans for securing the cuff to the surrounding tissue.
 4. A cuffaccording to claim 3 wherein the securing means comprises a pair of tabssecured one at each end of a transverse portion that extends outwardlyfrom either side of the band.
 5. A cuff according to claim 1 or claim 2wherein said loop means adjacent said one end of the band is spaced fromthe band so as to receive said overlapping end of the band within theloop.
 6. A cuff according to claim 5 wherein the band portion within theloop is secured to the loop to form the cuff of desired circumference.7. A cuff according to claim 1 or claim 2 wherein said loop meansadjacent said one end of the band is also used for attaching the band toan applicator.
 8. A cuff according to claim 1 or claim 2 wherein theband has at said one end connector means comprising an elongated strapof implantable material disposed transversely to the band, said straphaving inwardly directed slits that divide the connector means into aband attachment portion, free ends of the strap in the band attachmentportion being folded over one another to provide the loop means and anouter deformable portion.
 9. A cuff according to claim 8 wherein theouter deformable portion extends outwardly from each side of the bandand constitutes means for securing the cuff to the surrounding tissue.10. A cuff according to claim 9 wherein the securing means includes atab secured to or integral with each transverse portion.
 11. A cuffaccording to claim 9 wherein the band attachment portion includes a loopdisposed above the band.
 12. A cuff according to claim 1 wherein theimplantable material comprises a composite including a reinforcingfabric.
 13. A cuff according to claim 1 wherein the implantable materialis cured silicone rubber sheeting.
 14. A cuff according to claim 13wherein the cured silicone rubber sheeting is reinforced with a wovenpolyester.